Quite nice for your first composed piece ever.
I like how you include some imitation between the different saxophones.
Like ilv said, you have an interesting theme that can be developed in various ways.
Some feedback:
As a musician I like to have some indications how to interpret the music. For instance, I would personally prefer to have Allegro maestoso (100bpm) than only the tempo marking. However, this is just my opinion.
I know this is a sketch, but please add articulation markings in your final result! It will help the performers to understand the music.
There are some issues with fingering positions, which could be very akward to play:
M.11. Soprano. You should change the passage from written low C# to the other low C#, because the notes of this transition (C# - B - D# - C#) all have to be done with another pinky position.
The last point is that you have to consider if you want to let the soprano play the high F# in mm.15 - 17., because the upper notes of the soprano saxophone can be very sharp.
Well done and I hope that you find the feedback useful!